Conventionally, it is well known that a brake system which performs an ABS control, is employed with a fluid-pressure control valve capable of reducing, holding, and building up the wheel-brake cylinder pressure, a pump provided for sucking brake fluid drained into the reservoir during the pressure-reduction operation of the fluid-pressure control valve and for discharging the sucked brake fluid toward the upstream side of the fluid-pressure control valve, a damper device provided for dampening pulsation in the brake fluid discharged from the pump, and a motor provided for driving the above-mentioned pump.
One such brake system has been disclosed in Japanese Patent Provisional Publication No. 2-231253.
In the conventional brake system, a plunger, constructing a pump, is slidably accommodated in the housing so that the plunger is arranged in a direction perpendicular to the rotational axis of the motor. A damper and a reservoir are disposed in the housing. A motor is mounted on one side wall of the housing. As regards the structure of installation of the motor on the housing, mounting bolts are arranged parallel to the rotational axis of the motor in the direction perpendicular to the axial direction of the plunger. These mounting bolts are screw-threaded into the corresponding female screw holes opening at the side wall of the housing.
Now then, in recent years, it is desired to small-size and to lighten an unit for an ABS control from the viewpoint of easy mounting of the system on the automotive vehicle. The small-sizing and lightening would be achieved by planning an optimal lay-out of a plunger pump, a damper, a reservoir, and a fluid-pressure control valve, all disposed in the housing of the ABS unit.
On the other hand, in designing for a damper and a reservoir, a volumetric capacity necessary for the damper and a volumetric capacity necessary for the reservoir must be selected, accounting for an enhanced dampening effect with respect to the brake fluid pressure and for an enhanced pressure-reduction effect with respect to the brake fluid pressure. Thus, as a matter of course, the degree of the small-sizing of the damper and the reservoir is limited. As a measure of small-sizing the damper and the reservoir, these elements are located closer to each other in the housing, to enable reduction in the total size of the housing. In this case, it is necessary to prevent the position of each of screw-threaded holes for mounting bolts which are used to mount the motor on the housing from overlapping the installation position of the damper and the installation position of the reservoir. On the other hand, it is also necessary to provide a totally-balanced fastening force at the respective fixed points by properly arranging each mounting device containing a bolt and the corresponding female screw-threaded portion. It is difficult to optimally form screw holes in the housing, while satisfying all of the previously-noted necessary conditions.
Additionally, when the pump motor is driven during the operation of the previously-described plunger pump, the reaction force to the fluid pressure acts in the axial direction of the pump (or the axial direction of the plunger) on the compression stroke of the plunger. Furthermore, the reaction force transmits from the plunger to the rotational axis of the motor and acts in the direction perpendicular to the rotational axis. As a result of this, the rotational axis of the motor oscillates. There is an increased tendency for the system to vibrate. This produces noise in the system. In such a case, the greater the perpendicular distance of the fixed point of the mounting bolt mounting the motor on the housing with respect to the axial line of the pump (the axial line of the plunger), the smaller the rigidity of supporting the motor. It is disadvantageous to noise and vibrations.
Assuming that the fixed point of the motor is aligned with the axial line of the plunger, the rigidity of supporting the motor can be enhanced. It is advantageous to reduction in noise and vibrations. However, the screw holes threadably receiving the mounting bolts and the cylindrical bore accommodating therein the plunger are arranged in the direction of the rotational axis of the motor. Therefore, it is necessary to provide a housing size enough to form the screw hole in a space between the side wall of the housing and the cylindrical bore accommodating therein the plunger. There is a problem that the housing is large-sized.
It is, therefore, in view of the previously-described disadvantages of the prior art, an object of the present invention to provide a brake system which is capable of small-sizing the total size of the system and simultaneously reducing noise and vibrations, by disposing the fixed point of each of mounting bolts capable of mounting a motor on a housing at an optimal position, considering the lay-out of a damper and a reservoir arranged in the housing, in order to ensure a necessary volumetric capacity the damper and a necessary volumetric capacity of the reservoir.